Lighting device

ABSTRACT

A lighting device comprising at least one solid state light emitter and at least one luminescent element spaced from the light emitter, a surface of the luminescent element being at least twice as large as the illumination surface of the light emitter. Also, a lighting device comprising at least one solid state light emitter and at least one luminescent element spaced from the light emitter, a surface of the luminescent element surface being at least twice as large as and substantially parallel to the illumination surface of the light emitter. Also, a lighting device comprising at least one solid state light emitter and at least one luminescent element spaced from the light emitter, a surface area of a projection of the luminescent element being at least twice as large as a surface area of a projection of the light emitter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/570,712, filed Sep. 30, 2009 (now U.S. Patent Publication No.2010/0020532), the entirety of which is incorporated herein byreference.

U.S. patent application Ser. No. 12/570,712 is a continuation of U.S.patent application Ser. No. 11/614,180, filed Dec. 21, 2006.

This application claims the benefit of U.S. patent application Ser. No.11/614,180, filed Dec. 21, 2006 (now U.S. Patent Publication No.2007/0236911), the entirety of which is incorporated herein byreference.

This application claims the benefit of U.S. Provisional PatentApplication No. 60/753,138, filed Dec. 22, 2005, the entirety of whichis incorporated herein by reference.

This application claims the benefit of U.S. Provisional PatentApplication No. 60/831,775, filed Jul. 19, 2006, the entirety of whichis incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a lighting device, in particular, adevice which includes one or more solid state light emitters and one ormore luminescent materials (e.g., one or more phosphors). In aparticular aspect, the present invention relates to a lighting devicewhich includes one or more light emitting diodes, and one or moreluminescent materials.

BACKGROUND OF THE INVENTION

A large proportion (some estimates are as high as one third) of theelectricity generated in the United States each year goes to lighting.Accordingly, there is an ongoing need to provide lighting which is moreenergy-efficient. It is well-known that incandescent light bulbs arevery energy-inefficient light sources—about ninety percent of theelectricity they consume is released as heat rather than light.Fluorescent light bulbs are more efficient than incandescent light bulbs(by a factor of about 4) but are still quite inefficient as compared tosolid state light emitters, such as light emitting diodes.

In addition, as compared to the normal lifetimes of solid state lightemitters, incandescent light bulbs have relatively short lifetimes,i.e., typically about 750-1000 hours. In comparison, the lifetime oflight emitting diodes, for example, can generally be measured indecades. Fluorescent bulbs have longer lifetimes (e.g., 10,000-20,000hours) than incandescent lights, but provide less favorable colorreproduction. Color reproduction is typically measured using the ColorRendering Index (CRI) which is a relative measure of the shift insurface color of an object when lit by a particular lamp. Daylight hasthe highest CRI (of 100), with incandescent bulbs being relatively close(about 95), and fluorescent lighting being less accurate (70-85).Certain types of specialized lighting have relatively low CRI's (e.g.,mercury vapor or sodium, both as low as about 40 or even lower).

Another issue faced by conventional light fixtures is the need toperiodically replace the lighting devices (e.g., light bulbs, etc.).Such issues are particularly pronounced where access is difficult (e.g.,vaulted ceilings, bridges, high buildings, traffic tunnels) and/or wherechange-out costs are extremely high. The typical lifetime ofconventional fixtures is about 20 years, corresponding to alight-producing device usage of at least about 44,000 hours (based onusage of 6 hours per day for 20 years). Light-producing device lifetimeis typically much shorter, thus creating the need for periodicchange-outs.

Accordingly, for these and other reasons, efforts have been ongoing todevelop ways by which solid state light emitters can be used in place ofincandescent lights, fluorescent lights and other light-generatingdevices in a wide variety of applications. In addition, where lightemitting diodes (or other solid state light emitters) are already beingused, efforts arc ongoing to provide light emitting diodes (or othersolid state light emitters) which are improved, e.g., with respect toenergy efficiency, color rendering index (CRI), contrast, efficacy(1m/W), and/or duration of service.

A variety of solid state light emitters are well-known. For example, onetype of solid state light emitter is a light emitting diode. Lightemitting diodes are well-known semiconductor devices that convertelectrical current into light. A wide variety of light emitting diodesare used in increasingly diverse fields for an ever-expanding range ofpurposes.

More specifically, light emitting diodes are semiconducting devices thatemit light (ultraviolet, visible, or infrared) when a potentialdifference is applied across a p-n junction structure. There are anumber of well-known ways to make light emitting diodes and manyassociated structures, and the present invention can employ any suchdevices. By way of example, Chapters 12-14 of Sze, Physics ofSemiconductor Devices, (2d Ed. 1981) and Chapter 7 of Sze, ModernSemiconductor Device Physics (1998) describe a variety of photonicdevices, including light emitting diodes.

The expression “light emitting diode” is used herein to refer to thebasic semiconductor diode structure (i.e., the chip). The commonlyrecognized and commercially available “LED” that is sold (for example)in electronics stores typically represents a “packaged” device made upof a number of parts. These packaged devices typically include asemiconductor based light emitting diode such as (but not limited to)those described in U.S. Pat. Nos. 4,918,487; 5,631,190; and 5,912,477;various wire connections, and a package that encapsulates the lightemitting diode.

As is well-known, a light emitting diode produces light by excitingelectrons across the band gap between a conduction band and a valenceband of a semiconductor active (light-emitting) layer. The electrontransition generates light at a wavelength that depends on the band gap.Thus, the color of the light (wavelength) emitted by a light emittingdiode depends on the semiconductor materials of the active layers of thelight emitting diode.

Although the development of light emitting diodes has in many waysrevolutionized the lighting industry, some of the characteristics oflight emitting diodes have presented challenges, some of which have notyet been fully met. For example, the emission spectrum of any particularlight emitting diode is typically concentrated around a singlewavelength (as dictated by the light emitting diode's composition andstructure), which is desirable for some applications, but not desirablefor others, (e.g., for providing lighting, such an emission spectrumprovides a very low CRI).

Because light that is perceived as white is necessarily a blend of lightof two or more colors (or wavelengths), no single light emitting diodecan produce white light. “White” light emitting diodes have beenproduced which have a light emitting diode pixel formed of respectivered, green and blue light emitting diodes. Other “white” light emittingdiodes have been produced which include (1) a light emitting diode whichgenerates blue light and (2) a luminescent material (e.g., a phosphor)that emits yellow light in response to excitation by light emitted bythe light emitting diode, whereby the blue light and the yellow light,when mixed, produce light that is perceived as white light.

In addition, the blending of primary colors to produce combinations ofnon-primary colors is generally well understood in this and other arts.In general, the 1931 CIE Chromaticity Diagram (an international standardfor primary colors established in 1931), and the 1976 CIE ChromaticityDiagram (similar to the 1931 Diagram but modified such that similardistances on the Diagram represent similar differences in color) provideuseful reference for defining colors as weighted sums of primary colors.

Light emitting diodes can thus be used individually or in anycombinations, optionally together with one or more luminescent material(e.g., phosphors or scintillators) and/or filters, to generate light ofany desired perceived color (including white). Accordingly, the areas inwhich efforts are being made to replace existing light sources withlight emitting diode light sources, e.g., to improve energy efficiency,color rendering index (CRI), efficacy (1m/W), and/or duration ofservice, are not limited to any particular color or color blends oflight.

A wide variety of luminescent materials (also known as lumiphors orluminophoric media, e.g., as disclosed in U.S. Pat. No. 6,600,175, theentirety of which is hereby incorporated by reference) are well-knownand available to persons of skill in the art. For example, a phosphor isa luminescent material that emits a responsive radiation (e.g., visiblelight) when excited by a source of exciting radiation. In manyinstances, the responsive radiation has a wavelength which is differentfrom the wavelength of the exciting radiation. Other examples ofluminescent materials include scintillators, day glow tapes and inkswhich glow in the visible spectrum upon illumination with ultravioletlight.

Luminescent materials can be categorized as being down-converting, i.e.,a material which converts photons to a lower energy level (longerwavelength) or up-converting, i.e., a material which converts photons toa higher energy level (shorter wavelength).

Inclusion of luminescent materials in LED devices has been accomplishedby adding the luminescent materials to a clear encapsulant material(e.g., epoxy-based or silicone-based material) as discussed above, forexample by a blending or coating process.

For example, U.S. Pat. No. 6,963,166 (Yano '166) discloses that aconventional light emitting diode lamp includes a light emitting diodechip, a bullet-shaped transparent housing to cover the light emittingdiode chip, leads to supply current to the light emitting diode chip,and a cup reflector for reflecting the emission of the light emittingdiode chip in a uniform direction, in which the light emitting diodechip is encapsulated with a first resin portion, which is furtherencapsulated with a second resin portion. According to Yano '166, thefirst resin portion is obtained by filling the cup reflector with aresin material and curing it after the light emitting diode chip hasbeen mounted onto the bottom of the cup reflector and then has had itscathode and anode electrodes electrically connected to the leads by wayof wires. According to Yano '166, a phosphor is dispersed in the firstresin portion so as to be excited with the light A that has been emittedfrom the light emitting diode chip, the excited phosphor producesfluorescence (“light B”) that has a longer wavelength than the light A,a portion of the light A is transmitted through the first resin portionincluding the phosphor, and as a result, light C, as a mixture of thelight A and light B, is used as illumination.

As noted above, “white LED lights” (i.e., lights which are perceived asbeing white or near-white) have been investigated as potentialreplacements for white incandescent lamps. A representative example of awhite LED lamp includes a package of a blue light emitting diode chip,made of gallium nitride (GaN), coated with a phosphor such as YAG. Insuch an LED lamp, the blue light emitting diode chip produces anemission with a wavelength of about 450 nm, and the phosphor producesyellow fluorescence with a peak wavelength of about 550 nm on receivingthat emission. For instance, in some designs, white light emittingdiodes are fabricated by forming a ceramic phosphor layer on the outputsurface of a blue light-emitting semiconductor light emitting diode.Part of the blue ray emitted from the light emitting diode chip passesthrough the phosphor, while part of the blue ray emitted from the lightemitting diode chip is absorbed by the phosphor, which becomes excitedand emits a yellow ray. The part of the blue light emitted by the lightemitting diode which is transmitted through the phosphor is mixed withthe yellow light emitted by the phosphor. The viewer perceives themixture of blue and yellow light as white light.

As also noted above, in another type of LED lamp, a light emitting diodechip that emits an ultraviolet ray is combined with phosphor materialsthat produce red (R), green (G) and blue (B) light rays. In such an LEDlamp, the ultraviolet ray that has been radiated from the light emittingdiode chip excites the phosphor, causing the phosphor to emit red, greenand blue light rays which, when mixed, are perceived by the human eye aswhite light. Consequently, white light can also be obtained as a mixtureof these light rays.

Designs have been provided in which existing LED component packages andother electronics are assembled into a fixture. In such designs, apackaged LED is mounted to a circuit board, the circuit board is mountedto a heat sink, and the heat sink is mounted to the fixture housingalong with required drive electronics. In many cases, additional optics(secondary to the package parts) are also necessary.

In substituting light emitting diodes for other light sources, e.g.,incandescent light bulbs, packaged LEDs have been used with conventionallight fixtures, for example, fixtures which include a hollow lens and abase plate attached to the lens, the base plate having a conventionalsocket housing with one or more contacts which are electrically coupledto a power source. For example, LED light bulbs have been constructedwhich comprise an electrical circuit board, a plurality of packaged LEDsmounted to the circuit board, and a connection post attached to thecircuit board and adapted to be connected to the socket housing of thelight fixture, whereby the plurality of LEDs can be illuminated by thepower source.

There is an ongoing need for ways to use solid state light emitters,e.g., light emitting diodes, in a wider variety of applications, withgreater energy efficiency, with improved color rendering index (CRI),with improved efficacy (1m/W), and/or with longer duration of service,for all possible light colors, including white light (including lightperceived as white light).

BRIEF SUMMARY OF THE INVENTION

As indicated above, in conventional LED packages which employ aluminescent material in order to provide light of one or more particularcolor hues, the LEDs are typically covered with an encapsulant, e.g., acured polymeric resin, in which a luminescent material, e.g., aphosphor, has been dispersed.

In addition, as described in U.S. patent application Ser. No.60/752,753, filed on Dec. 21, 2005, entitled “Lighting Device”(inventors: Gerald H. Negley, Antony Paul Ven de Ven and Neal Hunter),the entirety of which is hereby incorporated by reference, lightingdevices have been developed which employ solid state light emitters(e.g., light emitting diode chips) and luminescent material, in whichthe solid state light emitters (e.g., chips) are mounted on housings.

The general object of the present invention is to maximize the lightextraction from the solid state light emitter (e.g., light emittingdiode chip) or the package (e.g., LED package) in such devices.

In the case of conventional LED packages which include a phosphor, asignificant proportion (e.g., in many cases, as much as 20% to 25%) ofthe excitation light (i.e., light from the LED) is reflected (backscattered) from the phosphor back into the light emitting diodechip/package. Back scattered light which is scattered back into thelight emitting diode chip itself has a very low probability of coiningout of the chip, and hence, such back scattering results in a systemloss of energy.

In addition, the phosphor converted light is omni-directional, so thatin general, 50% of the light is directed back to the LED source.

Furthermore, if the luminescent element is too thick, and/or if theluminescent material (e.g., phosphor) content in the luminescent elementis too great, “self-absorption” may occur. Self-absorption occurs whenlight emissions within the packaging layer stay within the packaginglayer to excite other phosphor particles and eventually are absorbed orare otherwise prevented from exiting the device, thus reducingperformance (intensity) and efficiency. Additionally, if the particlesize of the luminescent material (e.g., phosphors) is too large, theparticles of luminescent material can cause unwanted scattering of boththe excitation source (the LED chip) and the light generated by thephosphor.

In accordance with one aspect of the present invention, by spatiallyseparating the solid state light emitter from the luminescent element,this extraction efficiency can be improved. In addition, by making thesurface area of the illumination surface of the solid state lightemitter which faces the luminescent element much smaller than thesurface area of the luminescent element which faces the solid statelight emitter, any backscatter light from the excitation source or anyemitted light from the luminescent element has a lower probability ofreabsorption in the solid state light emitter.

In accordance with a first aspect of the present invention, there isprovided a lighting device comprising at least one solid state lightemitter and at least one luminescent element, in which the luminescentelement comprises at least one luminescent material and is spaced fromthe solid state light emitter. In this aspect of the invention, aluminescent element surface of the luminescent element has a surfacearea which is at least twice as large (in some embodiments at least fivetimes as large, and in some embodiments at least ten times as large) asan illumination surface of the solid state light emitter.

In a specific feature according to this aspect, the luminescent elementis spaced from the solid state light emitter by a distance which is atleast equal to a largest dimension of the illumination surface.

In a specific feature according to this aspect, the luminescent elementis spaced from the solid state light emitter by a distance in the rangeof from about 100 micrometers to about 750 micrometers (for example,from about 500 micrometers to about 750 micrometers, e.g., about 750micrometers).

In accordance with a second aspect of the present invention, there isprovided a lighting device comprising at least one solid state lightemitter and at least one luminescent element, in which the luminescentelement comprises at least one luminescent material and is spaced fromthe solid state light emitter. In this aspect of the invention, thesolid state light emitter has an illumination surface facing theluminescent element and the luminescent element has a luminescentelement surface facing the solid state light emitter. In addition, inthis aspect of the invention, the luminescent element surface issubstantially parallel to the illumination surface, and the luminescentelement surface has a surface area which is at least twice as large (insome embodiments at least five times as large, and in some embodimentsat least ten times as large) as the surface area of the illuminationsurface.

In a specific feature according to this aspect, the luminescent elementis spaced from the solid state light emitter by a distance which is atleast equal to a largest dimension of the illumination surface.

In accordance with a third aspect of the present invention, there isprovided a lighting device comprising at least one solid state lightemitter and at least one luminescent element, in which the luminescentelement comprises at least one luminescent material and the luminescentelement is spaced from the solid state light emitter.

In this aspect, an imaginary first flat shape is defined by a set ofluminescent element points, each of the luminescent element points beinglocated in an x-y plane oriented relative to a z axis which passesthrough a center of the solid state light emitter and a center of theluminescent element and having x, y coordinates which correspond, foreach radial position relative to the z axis, to x, y coordinates of apoint on the luminescent element which is the farthest from the z axisat such radial location, i.e., the first flat shape is a projection ofthe luminescent element onto a plane which is perpendicular to the zaxis connecting the respective centers of the luminescent element andthe solid state light emitter. An imaginary second flat shape is definedby a set of light emitter points, each of the light emitter points beinglocated in an x-y plane oriented relative to the z axis and having x, ycoordinates which correspond, for each radial position relative to the zaxis, to x, y coordinates of a point on the solid state light emitterwhich is the farthest from the z axis at such radial location i.e., thesecond flat shape is a projection of the solid state light emitter ontoa plane which is perpendicular to the z axis. In this aspect, the areaof the first flat shape is at least twice as large (in some embodimentsat least five times as large, and in some embodiments at least ten timesas large) as the area of the second flat shape (where more than onesolid state light emitter is present in the lighting device, the solidstate light emitter in the above comparison being the one that has thelargest second flat shape of any solid state light emitter in thelighting device).

In a specific feature according to this aspect, the luminescent elementis spaced from the solid state light emitter by a distance which is atleast equal to a largest dimension of the second flat shape.

In a further specific feature according to the present invention, thesolid state light emitter is a light emitting diode chip.

In a further specific feature according to the present invention, thesolid state light emitter has an illumination surface which issubstantially planar.

In a further specific feature according to the present invention, theluminescent element has a luminescent surface which is substantiallyplanar.

In a further specific feature according to the present invention, theluminescent element comprises a matrix (e.g., which may be a polymericmaterial, which may have been cured) in which a luminescent material iscontained.

In a further specific feature according to the present invention, aluminescent material is contained in the luminescent element in anamount which is not greater than about 15% by volume.

In a further specific feature according to the present invention, theluminescent element comprises at least one phosphor.

In a further specific feature according to the present invention, theluminescent element comprises particles of luminescent material whichhave an average particle size of not greater than 50 microns.

In a further specific feature according to the present invention, athickness of the luminescent element is not greater than 1 cm.

In a specific aspect, the lighting device is one that can produce lightthat is perceived as “white”.

The invention may be more fully understood with reference to theaccompanying drawings and the following detailed description of theinvention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a schematic illustration depicting an embodiment of a lightingdevice 10 in accordance with the present invention.

FIG. 2 depicts a light emitting diode and a luminescent element in orderto further explain the terminology set forth above regarding the thirdaspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, in accordance with various aspects of the presentinvention, there is provided a lighting device comprising at least onesolid state light emitter and at least one luminescent element, theluminescent element comprising at least one luminescent material.

Any desired solid state light emitter or emitters can be employed inaccordance with the present invention. Persons of skill in the art areaware of, and have ready access to, a wide variety of such emitters.Such solid state light emitters include inorganic and organic lightemitters. Examples of types of such light emitters include lightemitting diodes (inorganic or organic), laser diodes and thin filmelectroluminescent devices, a variety of each of which are well-known inthe art. As noted above, a wide variety of luminescent materials (alsoknown as lumiphors or luminophoric media, e.g., as disclosed in U.S.Pat. No. 6,600,175, the entirety of which is hereby incorporated byreference) are well-known and available to persons of skill in the art,and any such materials can be used in accordance with the presentinvention.

In one aspect of the present invention, there is provided a device whichcomprises at least first and second solid state light emitters, in whichthe first solid state light emitter emits light of a first wavelengthand the second solid state light emitter emits light of a secondwavelength, the second wavelength differing from the first wavelength.In such a device, the solid state light emitters can emit light of anydesired wavelength or wavelengths (or wavelength range or wavelengthranges) within the ranges of infrared, visible and ultraviolet light,including, e.g., (1) two or more light emitting diodes emitting lightwithin different wavelength ranges within the visible spectrum, (2) twoor more light emitting diodes emitting light within different wavelengthranges within the infrared spectrum, (3) two or more light emittingdiodes emitting light within different wavelength ranges within theultraviolet spectrum, (4) one or more light emitting diodes emittinglight within the visible spectrum and one or more light emitting diodesemitting light within the infrared spectrum, (5) one or more lightemitting diodes emitting light within the visible spectrum and one ormore light emitting diodes emitting light within the ultravioletspectrum, etc.

As noted above, persons skilled in the art are familiar with a widevariety of light emitters, including a wide variety of light emittingdiodes, a wide variety of laser diodes and a wide variety of thin filmelectroluminescent devices, and therefore it is not necessary todescribe in detail such devices, and/or the materials out of which suchdevices are made.

As indicated above, the lighting devices according to the presentinvention can comprise any desired number of solid state emitters. Forexample, a lighting device according to the present invention caninclude 50 or more light emitting diodes, or can include 100 or morelight emitting diodes, etc. In general, with current light emittingdiodes, greater efficiency can be achieved by using a greater number ofsmaller light emitting diodes (e.g., 100 light emitting diodes eachhaving a surface area of 0.1 mm² vs. 25 light emitting diodes eachhaving a surface area of 0.4 mm² but otherwise being identical).

Analogously, light emitting diodes which operate at lower currentdensities are generally more efficient. Light emitting diodes which drawany particular current can be used according to the present invention.In one aspect of the present invention, light emitting diodes which eachdraw not more than 50 milliamps are employed.

The solid state light emitters and luminescent elements in the lightingdevices of the present invention can be arranged, mounted and suppliedwith electricity in any desired manner, and can be mounted on anydesired housing or fixture, and the solid state light emitters can besupplied with electricity in any desired manner. Skilled artisans arefamiliar with a wide variety of arrangements, mounting schemes, powersupplying apparatuses, housings and fixtures, and any such arrangements,schemes, apparatuses, housings and fixtures can be employed inconnection with the present invention. The lighting devices of thepresent invention can be electrically connected (or selectivelyelectrically connected) to any desired power source, persons of skill inthe art being familiar with a variety of such power sources.

Representative examples of arrangements of solid state light emittersand luminescent elements, schemes for mounting solid state lightemitters and luminescent elements, apparatus for supplying electricityto solid state light emitters, housings for solid state light emittersand luminescent elements, fixtures for solid state light emitters andluminescent elements and power supplies for solid state light emitters,all of which are suitable for the lighting devices of the presentinvention, are described in U.S. patent application Ser. No. 60/752,753,filed concurrently herewith, entitled “Lighting Device” (inventors:Gerald H. Negley, Antony Paul Ven de Ven and Neal Hunter), the entiretyof which is hereby incorporated by reference. Such fixtures also make itpossible to integrate excellent thermal dissipation into the lightfixture itself.

In some embodiments of the lighting devices according to the presentinvention, the lighting device comprises a housing which has a highlyreflective element having tapered walls, e.g., the device comprisesreflective walls which define a truncated cone (frustoconical shape). Ithas been observed, in accordance with the present invention, that theoverall extraction efficiency (through the optic) can be improved byincluding such a reflective element having tapered walls.

In some embodiments of the lighting devices according to the presentinvention, the lighting device comprises a housing which has a highlyreflective element having substantially straight walls, e.g., the devicecomprises reflective walls which define a cylinder.

The expression “on”, e.g., as used above in the expression “mounted on”,means that the first structure which is “on” a second structure can bein contact with the second structure, or can be separated from thesecond structure by one or more intervening structures.

A statement herein that items are “electrically connected,” means thatthere are no components electrically between the items, the insertion ofwhich materially affect the function or functions provided by thedevice. For example, two items can be referred to as being electricallyconnected, even though they may have a small resistor between them whichdoes not materially affect the function or functions provided by thedevice (indeed, a wire connecting two items can be thought of as a smallresistor); likewise, two items can be referred to as being electricallyconnected, even though they may have an additional electrical itembetween them which allows the device to perform an additional function,while not materially affecting the function or functions provided by adevice which is identical except for not including the additional item;similarly, two items which are directly connected to each other, orwhich are directly connected to opposite ends of a wire or a trace on acircuit board or another medium, are electrically connected.

The one or more luminescent materials can be any desired luminescentmaterial. As noted above, persons skilled in the art are familiar with,and have ready access to, a wide variety of luminescent materials. Theone or more luminescent materials can be down-converting orup-converting, or can include a combination of both types.

For example, the one or more luminescent materials can be selected fromamong phospors, scintillators, day glow tapes, inks which glow in thevisible spectrum upon illumination with ultraviolet light, etc.

The one or more luminescent materials, when included, can be provided inany desired form. For example, in one aspect, a lighting deviceaccording to the present invention can comprise at least one luminescentelement which comprises the first luminescent material, the luminescentelement being attached to a housing, the luminescent element and thehousing defining an internal space, at least one of the solid statelight emitters being positioned within the internal space.

The luminescent element can, if desired, comprise a material in whichthe first luminescent material is embedded. For example, persons ofskill in the art are very familiar with luminescent elements comprisinga luminescent material, e.g., a phosphor, embedded in a resin (i.e., apolymeric matrix), such as a silicone material or an epoxy material.

In a preferred aspect of the present invention, the lighting devicecomprises at least one luminescent element which comprises at least afirst luminescent element region and a second luminescent elementregion, the first luminescent element region comprising a firstluminescent material, the second luminescent element region comprising asecond luminescent material, the first luminescent material, upon beingexcited, emitting light of a first wavelength (or range of wavelengths),the second luminescent material, upon being excited, emitting light of asecond wavelength (or range of wavelengths), the second wavelength (orrange of wavelengths) differing from the first wavelength (or range o fwavelengths).

In accordance with another preferred aspect of the invention, a lightingdevice can comprise a plurality of luminescent elements, eachluminescent element comprising at least one luminescent material, eachluminescent element being attached to a housing to define an internalspace, at least one solid state light emitter being positioned withineach internal space.

In embodiments of the present invention in which a plurality of solidstate light emitters are mounted on a housing, the heat load produced bythe solid state light emitters is distributed over the surface of thehousing. The more uniformly the solid state light emitters aredistributed over the surface area of the housing, the more uniformly theheat load is distributed. As a result, the housing can provide moreefficient heat dissipation, with the result that the housing can, ifdesired, be made smaller than would otherwise be the case.

In addition, by having multiple solid state light emitters (as opposedto a single point source of light), the light source is affected less byshadowing—that is, if an object which is smaller than the light emittingarea is placed in front of the light emitting area, only a portion ofthe light rays would be blocked. Since the light sources follow theHuygens principle (each source acts as a spherical wave front), theviewing of a shadow is not seen, and only a slight dimming of theilluminated source is seen (in contrast to where a single filament isemployed, where the light would be substantially dimmed and a shadowwould be observed).

The devices according to the present invention can further comprise oneor more long-life cooling device (e.g., a fan with an extremely highlifetime). Such long-life cooling device(s) can comprise piezoelectricor magnetorestrictive materials (e.g., MR, GMR, and/or HMR materials)that move air as a “Chinese fan”. In cooling the devices according tothe present invention, typically only enough air to break the boundarylayer is required to induce temperature drops of 10 to 15 degrees C.Hence, in such cases, strong “breezes” or a large fluid flow rate (largeCFM) are typically not required (thereby avoiding the need forconventional fans).

The devices according to the present invention can further comprisesecondary optics to further change the projected nature of the emittedlight. Such secondary optics are well-known to those skilled in the art,and so they do not need to be described in detail herein—any suchsecondary optics can, if desired, be employed.

The devices according to the present invention can further comprisesensors or charging devices or cameras, etc. For example, persons ofskill in the art are familiar with, and have ready access to, deviceswhich detect one or more occurrence (e.g., motion detectors, whichdetect motion of an object or person), and which, in response to suchdetection, trigger illumination of a light, activation of a securitycamera, etc. As a representative example, a device according to thepresent invention can include a lighting device according to the presentinvention and a motion sensor, and can be constructed such that (1)while the light is illuminated, if the motion sensor detects movement, asecurity camera is activated to record visual data at or around thelocation of the detected motion, or (2) if the motion sensor detectsmovement, the light is illuminated to light the region near the locationof the detected motion and the security camera is activated to recordvisual data at or around the location of the detected motion, etc.

FIG. 1 is a schematic illustration depicting an embodiment of a lightingdevice 10 in accordance with the present invention. The lighting devicedepicted in FIG. 1 includes a fixture 11 (shown schematically) basedwith a blue light source (one or more light emitting diodes) and highlyreflective surfaces, a phosphor and scattering layer 12 having a surfacearea which is larger than the light emitting diode(s) (the phosphorgenerating yellow light, upon excitation from light from the lightemitting diode), and a pair of brightness enhancement films 13 and 14,with uniform white light 15 exiting the lighting device 10.

Brightness enhancement films are well-known in the art and are readilyavailable. Brightness enhancement films (e.g., BEF films commerciallyavailable from 3M) are optional—when employed, they provide a moredirectional light source by limiting the acceptance angle. Light not“accepted” is recycled by the highly reflective light source enclosure.The scattering layer is also optional. The scattering layer can beincluded in the phosphor layer, and/or a separate scattering layer canbe provided. A wide variety of separate scattering layers and combinedluminescent and scattering layers are well known to those of skill inthe art, and any such layers can be employed in the lighting devices ofthe present invention.

In sonic embodiments in which there is included a brightness enhancementfilm (which can optionally be replaced by one or more extraction films,such as by WFT), the brightness enhancement film is optimized to limitthe viewing angle of the emitted source and to increase the probabilityof extracting light on the first (or earliest possible) pass.

In some embodiments of the lighting devices according to the presentinvention, the lighting device comprises a diffuser which provides photorecycling within a particular extraction angle, with losses which areless than those typically associated with BEF films. Some such diffusersdiffuse and scatter light. An example of such a phot recycling diffuseris the “Engineered Diffuser”™ available from RPC Photonics.

Preferably, one or more surfaces of the fixture (e.g., the housing) arereflective, so that light from some or all of the solid state lightemitters, e.g., light emitting diodes, is reflected by such reflectivesurfaces.

FIG. 2 depicts a light emitting diode 20 and a luminescent element 21which are oriented relative to one another in a way such that they donot have respective surfaces facing one another, in order to furtherexplain the terminology set forth above regarding the third aspect ofthe present invention.

As noted above, in the third aspect of the present invention, a first(imaginary) flat shape 22 is defined by a set of luminescent elementpoints, each of the luminescent element points being located in an x-yplane 23 oriented relative to a z axis 24 which passes through a center25 of the light emitting diode and a center 26 of the luminescentelement and having x, y coordinates which correspond, for each radialposition relative to the z axis, to x, y coordinates of a point on theluminescent element which is the farthest from the z axis at such radiallocation, i.e., the first flat shape is a projection of the luminescentelement onto a plane which is perpendicular to the z axis connecting therespective centers of the luminescent element and the solid state lightemitter. A second (imaginary) flat shape 27 is defined by a set of lightemitter points, each of the light emitter points being located in an x-yplane oriented relative to the z axis and having x, y coordinates whichcorrespond, for each radial position relative to the z axis, to x, ycoordinates of a point on the solid state light emitter which is thefarthest from the z axis at such radial location i.e., the second flatshape is a projection of the solid state light emitter onto a planewhich is perpendicular to the z axis. In the third aspect of the presentinvention, the area of the first flat shape 22 is at least twice aslarge as the area of the second flat shape 27.

Any two or more structural parts of the lighting devices describedherein can be integrated. Any structural part of the lighting devicesdescribed herein can be provided in two or more parts (which can be heldtogether, if necessary).

The invention claimed is:
 1. A lighting device comprising: at least onesolid state light emitter; and at least one luminescent element, theluminescent element comprising particles of at least a first luminescentmaterial, the luminescent element spaced from the solid state lightemitter, a content of luminescent material in the luminescent elementnot greater than about 15% by volume, the particles of the firstluminescent material having an average particle size of not greater than50 microns, and a thickness of the luminescent element not greater than1 cm.
 2. A lighting device as recited in claim 1, wherein: the solidstate light emitter has an illumination surface, the luminescent elementhas a luminescent element surface, the luminescent element surface is atleast twice as large as the illumination surface.
 3. A lighting deviceas recited in claim 1, wherein: the solid state light emitter has anillumination surface, the luminescent element is spaced from the solidstate light emitter by a distance which is at least equal to a largestdimension of the illumination surface.
 4. A lighting device as recitedin claim 1, wherein the solid state light emitter is a light emittingdiode chip.
 5. A lighting device as recited in claim 1, wherein: thesolid state light emitter has an illumination surface, the luminescentelement has a luminescent element surface, the luminescent elementsurface is at least five times as large as the illumination surface. 6.A lighting device as recited in claim 1, wherein: the solid state lightemitter has an illumination surface, the luminescent element has aluminescent element surface, the luminescent element surface is at leastten times as large as the illumination surface.
 7. A lighting device asrecited in claim 1, wherein: the solid state light emitter has anillumination surface, the luminescent element has a luminescent elementsurface, the illumination surface is substantially planar, and theluminescent element surface is substantially planar.
 8. A lightingdevice as recited in claim 1, further comprising at least one scatteringlayer.
 9. A lighting device as recited in claim 1, further comprising atleast one brightness enhancing film.
 10. A lighting device as recited inclaim 1, wherein the luminescent element is also a scattering layer. 11.A lighting device as recited in claim 1, wherein the luminescent elementis spaced from the solid state light emitter by a distance in the rangeof from about 100 micrometers to about 750 micrometers.
 12. A lightingdevice as recited in claim 1, wherein the luminescent element is spacedfrom the solid state light emitter by a distance in the range of fromabout 500 micrometers to about 750 micrometers.
 13. A lighting device asrecited in claim 1, wherein the luminescent element comprises a matrixin which a luminescent material is contained.
 14. A lighting device asrecited in claim 13, wherein the matrix comprises a polymeric material.15. A lighting device as recited in claim 14, wherein the polymericmaterial has been cured.
 16. A lighting device comprising: at least onesolid state light emitter; and at least one luminescent clement, theluminescent element comprising at least one luminescent material, acontent of the luminescent material in the luminescent element notgreater than about 15% by volume, the first luminescent materialcomprising particles having an average particle size of not greater than50 microns, the luminescent element spaced from the solid state lightemitter, the solid state light emitter having an illumination surface,and the luminescent element having a luminescent element surface, andthe luminescent element surface at least twice as large as theillumination surface.
 17. A lighting device as recited in claim 16,wherein the luminescent element is spaced from the solid state lightemitter by a distance which is at least equal to a largest dimension ofthe illumination surface.
 18. A lighting device as recited in claim 16,wherein: the illumination surface is substantially planar, and theluminescent element surface is substantially planar.
 19. A lightingdevice as recited in claim 16, wherein the luminescent element comprisesa matrix in which a luminescent material is contained.
 20. A lightingdevice as recited in claim 16, wherein the luminescent element surfaceis at least five times as large as the illumination surface.